Thread-chaser gauge



Sept. 26, 1950 c, CAMPBELL 2,523,277

THREAD-CHASER GAUGE Filed Nov. 7, 1946 I INVENTOR.

a 5k I BY CARL CAMPBELL I 22 20 A9 10 F/ 4 ATTORNEY Patented Sept. 26, 1950 UNITED STATES PATENT- OFFICE THREAD-CHASER GAUGE Carl E. Campbell, New York, N. Y. Application November 7, 1946, Serial No. 708,361

3 Claims. (01. 33-172) (Granted under the act of amended April 30, 1928;

This invention relates to gauges, and specifically to gauges for determining the position of cutting teeth on thread-chasers with respect to the reference surfaces thereof that establish the location of said thread-chasers when in use on a thread-cutting machine.

An object of this invention is to provide a gaug that is compact, sturdy, accurate, inexpensive, and easy to make and to use.

Another object is to provide a gauge for the determination of position of cutting teeth on thread-chasers, with a view to facilitating the selection of a group of said thread-chasers that will cooperate to form a set capable of cutting correct threads when installed on a threadcutting machine.

Further objects and advantages of this invention, as well as its construction, arrangement and operation, are apparent from the following description and claims in connection with the accompanying drawing, in which Fig. 1 is a perspective view of one embodiment of the invention,

Figs. 2 and 3 are cut-awayperspective views illustrating the use of the gauge shown in Fig. 1 in measuring radial and tangential thread-chasers, respectively, and

Fig. 4 is a sectional view taken along the longitudinal center line of the gauge.

Thread-cutting machines customarily utilize a holder or die-stock of substantially annular form, havingprovision at several points (usually four) around its periphery for mounting cutter bits that are ordinarily referred to as thread-chasers.

For the purpose of this description, it is assumed that the holder is adapted to receive four thread-chasers at 90 intervals, although it is apparent that all the factors involved can be related equally well to a holder for some other number of thread-chasers. Each thread-chaser is formed with a serrated edge adapted to cut a screw-thread of a particular pitch when urged against a revolving object such as a shaft. When a set of thread-chasers is installed in a holder, each one is positioned axially of the holder by the engagement of a groove or dovetail slot on the thread-chaser with a mating element formed in the holder. When a holder (die-stock) and its chasers are properly assembled, the threads, i. e., cutting teeth of chasers that in operation operate successively must, obviously, be fixedly positioned so that axially they are a quarter of a thread pitch apart.

Failure to conform to this requirement results March 3, 1883, as 370 0. G. 757) in a defective threading operation wherein two to four parallel helices are formed instead of one, and the spaces separating these helices are less than the desired pitch of a correct thread. Excessive metal is thus cut away, and the threaded member in cooperation with another member, for example a nut, cannot develop the full strength which is available with a correct thread.

the practice to market such thread-chasers in "matched sets wherein the component chasers differ from one another in tooth position by multiples of one quarter of a thread pitch. However, users of thread-chasers frequently find that one or more chasers in a set become lost, or broken or otherwise damaged, so as to be unavailable for further use. In the past, such an occurrence resulted in discarding the remainder of the set,

since satisfactory machine operation is not ob-' tained with less than a full set of chasers, and it has hitherto been'impracticable to replace missing or defective chasers.

The present invention enables the user to reconstitute complete sets, by facilitating the selection from a group comprised of broken sets or of previously unrelated individual chasers that bear the desired relationship to each other. The economic benefits accruing to the user by thus salvaging a substantial part of the expensive equipment formerly discarded are obvious.

The manner in which this is accomplished is evident from the following description and from the annexed drawing, in which I 0, l2, and II ar carefully finished and preferably hardened metal blocks in the general form 'of rectangular parallelepipeds, assembled to one another by some convenient means such as through use of screws is threaded into tapped holes l8. End block I4 is provided with a slot 20 fashioned transversely of the assembled fixture and adapted to carry bars 22, 24, that preferably have rectan gular cross-sections closely fitted to slot 20. One of the said bars, as 22, carries a pointer or index 26- that is shaped to conform to the type of teeth on the cutters to be measured, and that projects through aperture 34 in end block l4. The bars are frictionally retained in slot 20, for example by the urging of flat springs 26 under thrust exerted by thumbscrews 36. Pegs 32 seated in block I4 are provided to engage holes in the said flat springs 26 to prevent their rotation about thumbscrews 30. End block I4 is further provided with means for carrying a dial indicator 36 and comprised, for example, of spindle 38 carried by post 40 that is installed in hole 42 and secured therein by set-screw 44. Sensitive point 46 of dial indicator 36 is adapted to bear against the end of bar 22 and to transmit longitudinal motion thereof to the dial indicator, where the extent of such motion is indicated by rotation of pointer 48 with respect to th indicia incorporated on the face of the indicator. Obviously, other methods of indicating longitudinal displacement of bar 22 suggest themselves. such as by aflixing a scale thereto that is adapted to be read in conjunction with an index that can be fastened to end block I4 or to another part of the basic structure of the gauge, or by provision of a threaded member similar to that of a micrometer caliper.

Index 26 can be positioned at any of several levels by interchanging the positions of bars 22 and 24, especially if several such bars are provided instead of two, and in some arrangements of the combination of bars it is feasible to invert bar 22. Such flexibility is desirable in order to enable index 26 to be positioned approximately level with the upper surface of a radial threadchaser 50, since that upper surface represents the actual cutting face of the thread-chaser. Therefore, should manufacturing errors exist below the top surface of the thread-chaser, such errors do not contribute to a spurious indication of tooth position. Further height adjustment can be effected by employing flat stock or slab 52 upon which to place thread-chaser 50 in order to bring the top surface thereof substantially level with index 26. Flat stock 52 can be employed in several thicknesses according to the size of thread-chasers that are to be gauged.

In the case of tangential cutters such as that shown at 54 in Fig. 3, it is convenient to utilize a holder 56 adapted to support the tangential cutter in a specific position, as by engagement of dovetail 58, simulating the mounting of the cutter in an actual holder for use in a threading machine.

In use, a number of thread-chasers of one size are obtained, and, if they are radial cutters similar to 50, the positions of bars 22 and 24 are established so that index 26 is level with the top surface of a cutter 56 placed on the gauge, one or more pieces of flat stock 52 being employed between the cutter and base block ID, if desired, to adjust the height as closely as practicable.

.Sutficient pressure is exerted on bars 22, 24 by the lower surface of the thread-chaser. In the event of an error being present in this dimension on a particular cutter, allowance should be made for the discrepancy in interpreting the indicator reading presently to be obtained. The threadchaser is now urged forward until its serrated surface encounters index 26, meanwhile maintaining contact of surface 62 with side block l2, whereupon the index results to assume a position as in Fig. 2 where it projects into a space between two successive teeth and lodges in the center of such space. Should index 26 be initially out of alignment with the center of a space, thrust applied to thread-chaser 50 in a direction to cause greater depth of engagement of index 26 in the space will result in one or the other of the teeth adjacent to such space exerting a lateral thrust on the index to urge it into alignment with the center of the space. Any motion thus imparted to index 26 is communicated to bar 22 and thence to sensitive point 46 of dial indicator 36, causing a corresponding motion of pointer 48. The user observes the final indication registered on dial indicator 36 and makes a mental or written notation thereof. The foregoing procedure is repeated with each threadchaser in turn, so that ultimately each is identifled according to the displacement from'surface 62 and hence from reference slot 60 of a particular space between teeth on its cutting edge. By computing the desired progression of such amounts of displacement among the threadchasers of a set, or by referring to a prepared table, the user is enabled to group cutters into sets, the individual units of which cooperate in cutting a correct thread when employed on a machine for the purpose. Similarly, tangential cutters 54 (Fig. 3) can be measured and grouped into sets, but in this case it is necessary to support each cutter in a vertical position in order to present the serrated surface to index 26. This is done by providing holder 56 with a dovetail key to engage the dovetail slot of thread-chaser 54 as at 58. In use, the holder is urged against the surface of side block I2 and, while contact therewith is maintained, it is also urged forward until the serrated surface of thread-chaser 54 engages index 26 in the same manner as that previously described for radial cutter 50. The readings are taken and the results utilized in the manner previously described.

Optionally, a holder can be provided for radial cutters 50, to serve the same purpose that holder 56 does for tangential cutters 54, but such a holder is adapted to lie flat on base block Ill, and

\ would have a tongue on its upper surface adapted fiat springs 28 through the application of thumbscrews 30 to prevent the bars from moving inadvertently, but not so much pressure as to impede unduly the motion of bar 22 in response to thrust applied to index 26. Dial indicator 36 is adjusted on spindle 38 so that its sensitive point 46 bears against the end of bar 22. A threadchaser 50 is placed on base block I 0 or on flat stock 52, and urged against side block l2 until side surface 62 of the thread-chaser is firmly in contact therewith. It should be noted that surface 62 is finished at a standard distance for any particular size of cutter from locating-slot 60 on to fit groove 60 of the radial cutters. Use of such a holder would avoid any necessity for consideration of possible manufacturing errors arising from location of groove 60 at other than the standard distanc from surface 62 on radial thread-chasers.

It is to be understood that various modifications and changes can be made in this invention without departing from the spirit and scope thereof as set forth in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A gauge for thread chasers comprising a base block having a supporting surface for supporting the bottom of a thread chaser, a fixed side block having a reference surface substantially perpendicular to said supporting surface for locating a thread chaser, a fixed end block, a pointer mounted in said end block for sliding movement toward and away from said side block along a path substantially parallel to said supporting surface. said pointer extending into the space defined by said base block and said side block and said end block, means for adjusting said pointer toward and away from said supporting surface to adjust the location of said pointer relative to said supporting surface. spring means for normally restraining said pointer against movement, and an indicator responsive to movement of said pointer for indicating th position of said pointer relative to said surface.

2. A gauge for thread chasers comprising a substantially flat base block having a surface for supporting the bottom of a thread chaser, a fixed side block extending substantially perpendicularly away from said base block, said side block having a substantially fiat referenc surface intersecting said base-block surface for 10- cating a thread chaser, a fixed end block extending substantially perpendicularly away from said base block and substantially perpendicular to said side block, said end block having formed therein a U-slot substantially parallel to said base-block surface and substantially perpendicular to said reference surface, said slot extending from side to side of said end block and opening into the top of said end block, an aperture connecting said U-slot with the space defined by said base block and said side block and said end block, a pair of bars disposed one above the other in said U-slot for sliding movement, a pointer on one of said bars extending through said aperture, an indicator support on one of said blocks, an indicator, and means for adjusting said indicator on said support into contact with the bar carrying said pointer for indicating the position of said pointer relative to said reference surface.

3. A gauge comprising a base block having a supporting surface for supporting the bottom of a workpiece, a fixed side block having a reference surface substantially perpendicular to said supporting surface for locating a workpiece, a fixed end block, a pointer mounted in said end block for sliding movement toward and away from said side block along a path substantially parallel to said supporting surface, said pointer extending into the space defined by said base block and said side block and said end block, and an indicator responsive to movement of said pointer for indicating th position of said pointer relative to said surface.

CARL E. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,210,557 Stanbery Jan. 2, 1917 1,281,805 Metzger et a1 Oct. 15, 1918 1,456,938 Schoof May 29, 1923 1,901,242 Hogg Mar. 14, 1933 2,404,889 Ringie July 30, 1946 2,462,350 Bauer et al. Feb. 22, 1949 OTHER REFERENCES Pub.: Machinery, page 991. August, 1926. 

